Ballast structure for fluorescent lamps



March 29,- 1966 A. E. FEINBi-:RG r-:TAL 3,243,551

BALLAST STRUCTURE FLUORESCENT LAMPS 2 Sheets-Shea?l l Filed Oct'. l,1962 March 29, 1966 A, E. FEINBERG ETAL 3,243,651 BALLAST STRUCTURE FORFLUORESCENT LAMPS med oct. 1, 1962 2 sheets-sheet a j?? V572 for dZerfwzefy ya u ey second lamp thereafter ignites.

UnitedStates Patent )F BALLAST STRUCTURE FOR rLUoREsCENT l LAMPS AlbertE. Feinberg and Paul Berger, Chicago, Ill., assignors to AdvanceTransformer C0., Chicago, Ill., a corporationof Illinois Filed Oct. 1,1962, Ser. No. 227,469 8 Claims. (Ci.315'-187) .This'invention relatesgenerally to a ballast structure for gaseous discharge devices andmoreparticularly, is`

concerned with the construction of a ballast in which laminations which-form the core arelmade with a minimum of scrap.l The invention is alsoconcerned with a novel ballast for gaseous discharge devices including atransformer which has a secondary winding intended tocarry 4a `leadingcurrent.

a radical extent thatunless in. some way, prevented from4 e. -doing so,the ydevice will destroykitself. vThe ballasting provides thisdeterrent.

. Itnis wellknown in this art that a high leakage reactance transformerWill perform all `of the'desired functions mentioned above. The highleakage reactance transformer i-s one in which at least aprincipalsecondary winding is loosely` coupled relative to' the primarywinding so that although the benefits of transformation in accordancewith turns'ratio are available on open circuit, as soon as 'currentflows through the circuit, the high leakage reactance impedes the flowof current lowering the voltage across the load.

The ballast which will bevdescribed hereinafter and which comprises theinventionherein, is one which is intended for Vuse with fluorescentlighting lamps of the socalled` rapid-start variety. These lamps Ahavefilaments in their envelope 'ends which yare continuously 'energized andconsequently a ballast must also serve the function of providingcu'rrentcontinuously to these Iilaments. The

vlballast of the invention is constructed to provide such filamentwindings. e

Rapid-start-fluorescent lamps are normally operated in pairs, each' pairbeing served by a single ballast.v lThe circuit of the arrangement issuch that on open circuitfull output voltage of the ballast is appliedto one of the lamps because of a by-pass or shunt circuit across thesecond lamps Upon ignition of the first lamp, the current iiows throughthe shuntihg circuitoffhthe second lamp and produces a` voltage in acondenser in the shunt which raises the voltage across the lamp to suchan extent that the i Current then flows in series through bo'thof thelamps and the ballast windings. In order to provide good power factor inthe ballast as a whole, `a power factor correcting condenser is includedin series with the lamps. Thiscauses a leading current to flowrin thelprincipal secondary Winding of the ballast.

As described inU.S. PatentNo. 2,461,957, core saturation and resultingAwave shape distortion will occur in the -current flowing through thelamps unless one places a bridged' gap inthe magnetic circuit in thevicinity of the secondary winding which carries the leadingcurrent.

Attention is also invited to U.S. Patent No. 2,892,249 i which describesamethod of manufacturing a transformer core. It is contemplatedthat theballast of the invention herein will be manufactured in accordance withthe teachingsof the said AU.S. Patent No. 2,892,249. g

`length of the inward 3,243,651 Patented Mar. 29, 1966 lCe .gurationpunched matingly from strips of steeland thereafter rearranged to formthe necessary windows for the windings of the ballast. This will bebrought out in more detail hereinafter and reference may 'be had to thesaid' patent for additional information.

The center projection of the F-shaped laminations, in accordance withthe teachings of the said Patent 2,892,249,

*are punched intothe side edges of the elongate portion of the T-shapedlaminations so that when rearranged to form the core, the center windingleg has notches and the side legs have Ainward protrusions. Properadjustment of the protrusions provides the gaps for the shunt. By properchoice of dimension, the notches in the center winding leg will belocated on the interior ofthe secondary winding and thereby provide abridged gap in the center core giving the benefits of increasedefficiency, Igood lighting characteristics, etc.

This invention relates specifically to an improvement on the lastdescribed structure.

e The position of thebridge gap in the T-shaped, lamination, that is inAthecenter winding leg, was determined in the previous structure by theprovision of the shunt and the relative dimensions required in thewindows produced to accommodate the primary and secondary windings.

Heretofore it was believed that the dimensions of the resultingtransformer core were more or less limited because the distance betweenthe resulting shunt and the bridged gap controlled to a great extent thecharacteristics ofthe ballast. Attempts made to decrease the size andweight of the core, or to cut down on the amount of copper wire were notsuccessful. Problems arose in heating, Wave shape distortion and theballast was more expensive. As an important example, the structure abovereferred to which was devised for two 40watt rapid-start fluorescentlamps was a ballast having a transformer core formed -of laminations 4%inches long and a little over 2 inches fwide stacked .Sinch high. Thewidth of the center Winding leg was somewhat more than of an inch, thewidth of the side legs was a little more than 1/3 of aninch, the

-width of the bridgingy portions and hence the distance VVdecrease thelength of the core by one-half inch, decrease lthe. number of turns ofWire, and hence cut down on the size, weight and cost of the ballastwithout loss of lighting efficiency. A complete comparison of dimensionswill 'be set forth in describing the specfic example of the inventionhereinafter. e

The primary object of the invention is to provide a construction for aballast which will enable the achievement of advantages describedimmediately above.

In prior attempts to decrease the size of the ballast, as by merelyshortening the same, and making slight adjustments for the accommodationof the windings, it was found that the dis-tance between the shunt andbridged gap was insuiicient to give good operating characteristics.Magnetizing current increased requiring a heavier size of primarywinding wire to carry the added primary current. The lspace occupied bythe primary winding was thus increased and necessitated a completere-juggling of the f3 other dimensions which `could not practically bedone without added expense. A completely satisfactory design could notbe achieved in this manner.

Another attempt was made in which the shunt projec- Vtions were madelonger than usual to decrease the size of the high lreluctance gaps inthe shunt. It was thought that this would decrease the magnetizingcurrent, but it was found that too much flux was by-passed by the shuntgiving rise to a lower open circuit voltage with consequent bad startingcharacteristics. Attempts to increase open circuit voltage would requiremore turns of wire on the secondary winding, which in turn would changeoperating characteristics, -require changes in window dimension, etc.Furthermore, the metal removed from the bridged gap became excessivewith this expedient.

Still another attempt involved punching vthe F-shaped and T-shapedlaminations in a somewhat nested configuration but spaced lengthwise ofone another, so `that the displacement of the shunt from the bridged gapwhen the -core was assembled Was not the same as the width of thebridging ends. This produced a greater spacing between the shunt andbridged gap, but unfortunately it was 'found that the resulting increasein scrap offset the savings achieved by the resulting shorter ballast.

In accordance with the invention, the projections o'f `the F-shapedlaminations are formed with a narrow extension on their free ends, these.extensions approaching the opposite side edges of the central windingleg and being spaced therefrom by a high ,reluctance .air-gap ofordinary width. The notches thus removed from Ithe T- shaped laminationare of identical configuration so that .the 4bridged gap comprises apair of `aligned notches which are fairly wide but each having a narrowportion at its bottom end defining the narrow bridge therebetween.

Through the use of this type of structure, it was found that thelaminations may be kpunched fully nested without any scrap; that theclose proximity of the shunt and bridged gap did not result in anyincrease o'fmagnetizing current; that the crest factor and vlightingefficiency were excellent. It was found that the amount ,of copper wireneeded was decreased; that the resulting ballast was constructed at areduced cost; and that the ballast was quieter than heretofore.

Accordingly, other lobjects Vof the invention .are to achieve theadvantages mentioned by the structure describedabove.

The invention has been applied only to ballasts which are constructed bythe .method of Patent 2,892,249 and which are intended for use incircuits whereinV the secondary winding carries a leading current, butit is believed thatother ballasts .for circuits of this same ltype mayywell use the invention with advantage, even-thoughthe laminations arenot Stamped as nestedfgroups.

.Other objects of the invention and advantages will become apparent tothose skilled in this art as a preferred embodiment is described in somevdetail hereinafter, in connection with the drawings thereof.

' In the said drawings:

FIG. 1 is a diagrammatic top plan view of a transformer constructed inaccordance .with the invention and using the .novel core thereof,vthecoils of the apparatus being shown in section.

FIG. 2 is afragmentary top plan-view ofa strip o electrical steelshowingthe vlayout ofthe parts of the core of FIG. 1 along the same in order toillustrate the manner in which the laminations are punched from ,thestrip.

FIG. 3 isa View similar to that of FIG. 2 except in this case 'the stripof electrical steel is intended to pass through the punching machine ina direction at right angles to that of FIG. 2.

FIG. 4 is a circuit diagram of a ballast of the invention using thetransformer of FIG. 1.

The invention herein is characterized by the provision of a ballasthaving a core that is formed by the method lthat isdescribed in said`Patent 2,892,249, butin which the projections on the F-shapedlaminations, which will Y the bridged gap formed at such a locationyalong the length Aof the .center `winding leg so .that lit will AOccurunder a secondary Winding which carries a leading current. In additionto achieving the advantages of #high klighting eiciency, low current andAgood regulation, lsuch a construction provides flexibility of designand enables the manufacture of a highlylefficient ballasthaving anoverall length much less than heretofore.

IThe circuit diagram of the rapid-,start lighting arrangement with whichthe invention is intended to 'be used uis shown in FIG. 4. This circuit`isfconventional in all respects although the shunt and 'bridged gapresulting "from the invention should be understood to lbe different fromprevious structures.

In said FIG. 4, there isa ,transformer 10-which ,is designated bystraight lines indicating the conventional symbol for an iron corestructure. The gap yin the core structure at 12 indicates the bridgedjgap .of lthe 'invention which will be described hereinafter, .and the'lines ,representing lthe shuntat 14 represent the `shunt constructed.in accordance with the invention. The ,core of. the `transformer willbe designated 16.

There is a primary winding P which .is connected Yacross line terminals1.8` and 20 by suitable .leads A.r nark,e,d black and white andindicating the preference .respectively for the ungrounded and groundedline terminals. There .-is a secondary winding S which is mounted on thecorel ,16 separated from ,the primarywinding P `by the 4shunt 14 .butconnected `therewith lat ythe terminal 22. .A pair -of nuarescentdischarge lamps L1 vand L2, preferably of-,thesacalled rapid-startvariety, are :connected in `series ,withone Yanother by -the jumper 24and vthrough `the conductors 2,6

and 28 across boththe primary vand secondari/windings; The conductor 26extends to the junction 3.0 .which is .the left-hand terminal of theprimary winding -P., .and .the conductor 28 extends Ythrough the Ipowerfactorcondenser CPL to the right-hand-terminal ofthe secondary windingS, The circuit described is I,one `in which lthe Y,two lamps L1 and L2are connected in series with one another and together inautotransformer.connection withthe prim-any and lsecondary windings.Each of the lamps ,L1y and L2 has a 'filament sealed in therespectiveenvelope-ends `thereof as shown at F, and the filaments .areserved by -c-ontinuous flow of current through the medium v(1f-filamentwindings. F1, F2, and F3 mounted on the core lclosely coupled with theprimary Iwinding P and connected as shown. There is a shunting path 32around the lamp L2 which has a condenser CS infsaidpath.

Theoperation of this circuit is `well known but 4may briefly be.reviewed with'advantage. `Onyopen circuit, the total open circuitvoltageacross the primary and -secondary windings in additiverelationfappears -acrossfthe lamp 'L1 since the condenserfCs and Cp arenot effective in circuit `under `open circ-uit conditions. Ihe lampf1-.2

The resulting voltage is'suicient to `ignite -the ,lamp

,L1 and current immediately commences toflow'therein.

Since the 'lamp L2 ha-s notas yetbeen ignited, fit presents a veryhighimpedance to iow of currentsofthat all of the current of lamp L1will prefer to pass through-the condenser CS. As soon as the by-passpath 32 has current owing in it,'a voltageis produced inthe condenser CSwhich appear-s across the lamp L2 anldis sufcientito ignite the lamp.Thereafter current prefers the lamp L2 to the by-pass path l32,l and theresult-ing operating circuit consists of the two lamps L1 and'L2inseries with thepower factor condenser CP across `the primary andsecondary windings. The loose coupling between Vthe primary andsecondary windings provides the leakage reactance to prevent excessiveflow of current and keep the operating voltage to the desired level. Thepower factor condenser is needed so that the total power factor of theline 18 and 20 will be close to one hundred percent. Consequently, aleading current will flow in the secondary Winding. S.

FIG. 1 illustrates a transformer 10 constructed in .accordance with theinvention. The transformer is formed of a 'laminated iron core 16 whichhas a center T-shaped part 40 and two side parts, each of which will bedesignated 42, of F-shaped conguration.

The type of transformer core with which this invention is concerned isthat which is made of lam-inations punched from thin steel sheetingarranged in stacks and secured together.k The individual laminations areof course identical for any given part, and hence, no effort will bemade hereinafter to distinguish between the use-of the referencenumerals 40 and 42 to designate stacks or individual laminations ofidenticalcong-uration.

Ther T-shaped part 40 provides the center winding leg 44 of the core 16and its cross-head provides the lefthand bridging part 46. The F-shapedparts 42 provide the'side legs 48 which Iare parallel with the centerwinding leg 44 and spaced therefrom to form windows at 50 and 5,2.. TheF- shapedparts have their left-hand or straight ends `54 butted .againstthe cross-head or bridging part 46 at the joints 56 to close themagnetic circuit of the core 416 at the `left-hand end thereof. Theright-hand or inwardly projecting end l58 of the F-shaped parts 42extend inwardly of the core 16 toward and abut against the side edges of.the free end of the center winding leg 44 at 60to close the magneticcircuit thereat. The center inwardly extending projections 62 of theside legs 48 extend toward the center `wind-ing leg 44 and incooperation with a high reluctance gap 64 formed `thereat provide theshunt 1 4. The .windings P, F1, F2, and F3 are'rnounted in the window 52and the winding S is mounted in the-window 50. p Ituwilll be seen fromthe description above that the transformer 10 has its core 16 of theso-called shell variety with anlouyter rect-angular framing portion anda center winding leg. The parts are formed of stacks of laminations a-spreviously explained, and suitable notches 66 at the corners enable thecore 16 to be held together by clamps symbolically illustrated .at 68.

, As lpreviously mentioned, the laminati-ons 40 and 42 are formed by thescrapless method of Patent 2,892,249. A strip of suitable steel is runthrough a punch press at high speed, and the individual laminations arepunched out in nestedV configuratiomy Apair of F-shaped laminations 42are nested on opposite sides of a T-shaped lamination sothat the longinner edge of each of the F-shaped laminations is common with the longouter edge of the T-shaped lamination. Such groupings may be arrangededge to edge Ias shown in FIG. 2, then pas-sed through the machine inthe direction indicated by the arrow of FIG. 2. The only scrap whichresults will be the crosshatched portions marked S which, it will benoted, include punch-outs for the notches 66. In addition, there may bea narrow holding strip on oppos-ite edges of the wide metal strip inaccordance with normal high-speed punch press technique-s.

The orientation of the steel grain can be made parallel with the longdimension of the laminations by arranging the groupings of .a pair ofF-sh-aped laminations 42 and their inter-nested T-shaped lamination-s 40end to end along .a narrow strip as shown in FIG. 3 and passing thisstrip through the punching rriachiney in the direction as shown by thearrow to give rise to the scrap parts shown. A holding strip may also berequired along t-he edges of the strip of FIG. 3.

It will be appreciated that in arriving at the assembly of the core 16from a grouping such as shown in either FIG. 2 yor FIG. 3, the F-shapedparts are first moved 6 sideways away from the TJshaped part and thentranslated lengthwise thereof to the orientation shown. Consequently,for a complete absence yof scrap 4at the points designated A and B, inFIG. 2, for example, it is essential that the dimensions X, Y and Z inFIG.,1 be equal.

, When the core 16 is formed, there will be a notch 70 the brid-ged gap12. Likewise, the characteristics of the ballast in opera-tion will beaffected by the distance between the shunt 14 and t-he bridged gap 12.

As previously mentioned, through the medium of the invention, a ballastpreviously manufactured yand sold was considerably decreased in sizewith lattendant savings and improvement in operation. In laccordancewith the invention, each of the inward projections 62 ofthe side legs 48is provided with a narrow en-d extension 74, and resulting in a narrowrecess 76 being formed at the bottom of each lof the notches 70. Throughthis construction, the optimum bridge 72 readily may be established andthe width of the extensions 74 adjusted along with the gaps 64 foroptimum crest factor, magnetizing current, and lighting eiiiciency.

As previously indicated, in the prior structure Where projections 62were made very long in order to bring them close to the edge of thecenter winding leg, the resulting notches at 70 would be so deep as toleave insufficient iron at the bridging -center 72 to carry normal iiux.This would reduce the light output through peaking of the current wave.t When the extensions 74 with their resulting recesses 76 are used,there appeared to be no difficulty through distortion. It is believedthat sufficient iiux passed through the recesses 76 to give a goodcurrent wave shape. v

With this structure, thereforepthe configuration of the shunt could beused to achieve lower magnetizing current and lower primary current. Afair gap and the extensions 74 kept reluctance high enough to give goodopen circuit characteristics. It was found that the structure wasquieter than the previous structure, probably caused by by-passing moreflux at peak voltage wave.

A practical example of a ballast for operating two rapid-startfluorescent lamps will be described below, but in order to showthespeciiicadvantages of the invention, a comparison will be-made withthe previous structure. It will first be pointed out that the' samecapacitors Cs and CPF were used',.these lbeing .05 m.f.d. and 3.83m.f.d., respectively withl a l385 volts A.C. rating; the lamps were thesame, requiring about 430 milliamperesof current, gniting at about 260volts, and operatingat about volts. Live voltage wasV volts A.C. `at,60cycles. Lamp current was .400 ampere with-a crest factor of 1.35.Primary current was the same for both ballasts.

Ballasts for two A40-watt rapid-start fluorescent lamps Item orcharacteristic Previous Present Structure Structure Overall length ofcore 16 inehes. 4. 25 3. 74 Overall width of coredo- 21 17 2. 14 Widthoi center winding le do- 85 85 X, Y and Z do 385 .305 Width or'Projections 62 do. 188 200 Bridging distance 72 do 40 290 Gap 64 -do.085 040 Window Width do 310 320 Primary winding #26 gauge wir urns 790745 Secondary winding #27% gauge w .do 1, 455 1, 340 Filament windings#26 gauge wire do 26-29 25-28 Primary current amperes 620 580 Crestfactor 1. 35 1. 35

As indicated above, the structure of the invention has 7 beerifapplied`practically to ballasts for operating two 40 watt rapid startuorescentlamps, but there is no reason why the` advantagesl of.v theinvention should not be achieved in rapid-start or the like circuits ofdifferent kinds using one or more such lamps. Furthermore, althoughmostof t-heben'etits are p rovided when the laminations are 'stamped byscrapless methods, it is believed that the use' of shunting projectionswith narrow extensions combined with a bridged gap under a secondarywindingA carrying a leading current is new, especially where the lgap isformed by means of what might be termed notches of non-uniform width.

Accordingly, notwithstanding-the somewhat specific detail inthedescription hereinabove, it should be appreciatedthat variationsarepssible without departing from the spirit or scope of the inventionas defined'in the appended claims.

What` is desired to secure United States is;

1. A ballast` structure for igniting and` operating at least one gaseousdischarge device from an alternating current source and which comprisesa transformer having a core madeup of laminations of nestedconfigurations, butre-arranged to providea center T-shaped part formedof onel stackof laminations `and two outer F-shaped parts formed oftwo`additional stacks of laminations, but with the long legs ofthe partsspaced to provide winding windows, a pair ofA lateral projections one inthe center of each F-shaped part lextending across the space toward thelong leg of the T-shaped part but each projection having its free endterminatingshort of said longleg of the T- shapedpart to form gapsthereby and provide a shunt, said free ends being of substantiallylesser width than the respective projections to form narrow extensionsat said gaps respectively,` primary and secondary windings intransformer relation mounted on the long leg of the T- shaped part anddisposed in windows on opposite sides respectively ofy said. shunt, acondenser, first lead means for connecting the primary winding acrossthe source and second lead means for connectingI at least thesecondarywinding. in` series with the condenser and the discharge device,4 anotchin each edge of the long leg of the T- shaped` part under ,the secondarywinding and adjacent each projection, of a conguration and` ofdimensions substantially theA same asthe configuration and dimensionsofsaid adjacent projection.

2. A structure as claimed in claim 1 in which the primary and; secondarywindings are connected in autotransformer relationship.

3; A structure. as claimed in claim 1 in which every point on eachprojection is spaced from the equivalent pointr onVA its adjacent notch`by.: a distance measured along the length of-the long leg of theT-shaped` part which is substantially equal to the width of thecross-head of said T-shaped part.

4.. In a ballast construction for operating at least one gaseousdischarge device from an alternating current source, in which there isatransformer having a shell type core mounting a primary' winding and asecondary windby Letters Patent of the ing, .there being a shunt betweenthe windings and a bridged gap beneath the secondary winding, the corevbeing formed of a center T-shaped part and a pair ot in-i wardly facingouter F-shaped parts, the shunt being provided by the center projectionsof the F-,shaped parts extending toward the center T-shaped part butstopping short thereof to form gaps t-hereat, the bridged gap beingprovided by notches in the side edges of ythe center T-shaped vwidth attheir inner ends.

6. The invention as claimed in claim 4 in whichI the notches andIprojections including the extensions thereof are ofthe same dimensionsand configurations.

7. A fluorescent lamp ballast for igniting and operating at least a pairof lamps from an alternating current source, said lamps being connectedin series, said ballast including a transformer having a shell `typecore formed of a T-shaped center leg and F-shaped side legs, a primarywinding and a secondary winding mounted on the center leg and separatedby a shunt, the center projections of the F-shaped parts extendingtoward the center leg to provide said shunt and' being slightly spacedtherefrom to provide the gaps of the shunt, the windings beingconnectedin auto-transformer relation to said lamps, a power factor correctingcondenser in series with the secondary winding and effective duringoperation of the ballast to cause a leading current to flow in saidsecondary winding; a bridged' gap in the center leg beneath thesecondary winding, said gap being provided by notches cutting into thecenter windingleg from opposite edgcsth'ereof, the notches each havingan inner-most recess' the width of which is substantially less than theremainder of the notch, thereby reducing the amount ot iron inthe'bridge but the widthof the recesses being such as to permit somepassage of flux during operation to prevent undue saturation of thebridge. Y

8. A structure as claimed in claim 7 in which the center projectionshave a configuration and dimensions substantially the same as thenotches to provide extension tips on the ends thereof adjacent the gaps,respectively.

References Cited by the Examiner UNITED STATES PATENTS 3,114,861 12/1963Berger B15-109 GEORGE N. WESTBY, Primary Examiner, C, R, CAMPBELL,Assistant Examiner,

7. A FLUORESCENT LAMP BALLAST FOR IGNITING AND OPERATINGG AT LEAST APAIR OF LAMPS FROM AN ALTERNATING CURRENT SOURCE SAID LAMPS BEINGCONNECTED IN SERIES, SAID BALLAST INCLUDING A TRANSFORMER HAVING A SHELLTYPE CORE FORMED OF A T-SHAPED CENTER LEG AND F-SHAPED SIDE LEGS, APRIMARY WINDING AND A SECONDARY WINDING MOUNTED ON THE CENTER LEG ANDSEPARATED BY A SHUNT, THE CENTER PROJECTIONS OF THE F-SHAPED PARTSEXTENDING TOWARD THE CENTER LEG TO PROVIDE SAID SHUNT AND BEING SLIGHTLYSPACED THEREFROM TO PROVIDE THE GAPS OF THE SHUNT, THE WINDINGS BEINGCONNECTED IN AUTO-TRANSFORMER RELATION TO SAID LAMPS, A POWER FACTORCORRECTING CONDENSER IN SERIES WITH THE SECONDARY